Evaluation of the functionality of a traditional setting policy applied on directional earth fault function

High-impedance faults (HIFs) cannot be detected by the protective zones of distance relays. To overcome to this problem, a protective function called directional earth fault (DEF) function is included in numerical distance relays. To set the function some extensive calculations and probably some exhaustive simulations should be done. However, protection engineers usually utilize a traditional setting policy to make the setting easy. In this paper, we will have an evaluation on this setting policy to find out whether it can result in a proper operation of DEF function in detecting HIFs or not. To do this, using software MATLAB^®, we will simulate different HIFs on line Dogonbadan-Behbahan (a line of Iran transmission grid). Then the functionality of DEF function of the line relays which is set on the basis of the traditional setting policy will be evaluated in the presence of each HIF case. Eventually, for all simulated HIFs the impedance measured by the distance function of the line relays will be presented to show how HIFs affect the impedance location with respect to the protective zones.